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Varying shaft wall thickness optimizes golf club performance

Predicting a projectile’s path isn’t too difficult if you know the launch velocity and direction, if you know the constant for gravity, and if you can sketch a parabola. However, you don’t need to crack open a textbook and read up on physics to understand what’s going on. Anyone who has thrown a football or served a volleyball has learned how these forces interact to create a trajectory. In some sports, it gets a little more complicated when players use a stick, bat, or racquet to impart a much higher launch velocity. A hockey player uses the ice to bend the stick for an effective slap shot. A baseball player relies on the bat’s substantial mass and its length to send the ball over the heads of the outfielders and into the stands. A tennis player relies on the racquet’s mass and length, coupled with the strings’ elasticity, to serve an ace or send a blazing return past his or her opponent.

And then there’s golf. It should be the simplest of all sports. The player is stationary and the ball is stationary. The player can take his time in preparing a shot. A golfer doesn’t have to deal with the mayhem that occurs behind the line of scrimmage in every football play as the defensive tackles tear through the line to attempt a sack. Once the ball is in motion, its travel is unimpeded. No opposing team member is lurking around waiting for a chance to spike it or intercept it, and no goalie blocks the cup.

Perhaps these are the reasons that golf is among the most complex of all sports. The golfer’s swing is possibly the most focused, deliberate, and analyzed of all sports activities. However, success on a course doesn’t start with lessons. It starts with getting the right club into the golfer’s hands.

Join the Club

The importance of proper equipment selection can’t be overstated. Good technique is critical, as is the player’s strength, but a good fit matters much more. The optimal length is a start when a player is choosing a club, but the head’s lie and loft, which interact to provide the contact angle, are just as important as length. As the terms imply, the lie concerns the head’s sole, which determines the angle at which it lies when at rest on the ground, while the loft is the face angle.

The contact angle contributes to the trajectory. A trajectory that is too high wastes energy fighting gravity; one that is too low cuts the flight time too short. The club’s face also imparts a rotational component, or backspin, that provides a little extra lift, keeping the ball airborne longer than a ball with no rotation or a ball with forward spin. The club head’s center of gravity plays an important role in getting the ball off the ground at the right angle too.

And then there’s the shaft, which quite a bit of engineering is devoted to.

“A golf club shaft is an energy storage device,” said Scott Cokeing, director of engineering and global quality for True Temper Sports, Memphis, Tenn. (see Figure 1). The company has the lion’s share of the world market, manufacturing golf club shafts for such brands as AdamsGolf®, BridgestoneGolf®, Callaway®, Cleveland Golf®, Cobra®, Mizuno®, NikeGolf®, Ping®, TaylorMade®, Titleist®, TourEdge®, and Wilson Staff.

“Essentially, it’s a spring,” he said. “Some players put a lot of energy into their swing, so they need a relatively stiff shaft. Others put less energy into it, so they need a relatively flexible shaft.”

To the casual observer, golf club shafts don’t vary too much from one manufacturer to the next or one style to the next. The butt end usually measures about 0.600 in. OD and the tip end measures 0.375 in. OD, Cokeing said. Some have a smooth exterior and some have noticeable steps as the diameter changes, but this is about the extent of the differences.

A closer look, especially if that look included a view of the ID, would reveal something else altogether.

Figure 1
Scott Cokeing, True Temper’s director of engineering and global quality, inspects a dozen golf club shafts. The company estimates that its plant in Amory, Miss., has produced one billion shafts since it opened in 1964.

Choices, Choices. Sets of clubs are available in three styles. A constant-weight set consists of clubs of a single weight, regardless of length. In a descending set, the weight decreases as the club length decreases. In an ascending set, which is rare, the weight decreases as the club length increases.

Another factor is wall thickness. While a basic golf club shaft has a consistent wall thickness, True Temper’s forte is its ability to vary the wall thickness. Compared to a straight-pull shaft, which leaves little to the imagination, varying the shaft’s wall thickness is an engineer’s dream come true.

“The tip experiences a tremendous load, so this region has a thicker wall so the club won’t break,” Cokeing said. “The extra material also provides durability and performance. We use less material at the grip end, which doesn’t undergo nearly as much stress.” Decreasing the material at the grip also improves the feel of the club in the golfer’s hands, providing better feedback and control. The middle of the shaft has an intermediate thickness. Getting the thicknesses just right, and matching them to the golfer’s ability, can make the difference between a drive that leaves the head’s face at the maximum possible speed and something far slower. Optimizing the thicknesses also improves the golfer’s ability to send the ball straight down the fairway instead of a slice (to the right) or a hook (to the left).

The ability to adjust the wall thickness provides nearly endless latitude in changing the three main variables in shaft design, which ultimately affect the club’s performance: weight, stiffness, and flex point (or bend point, also known as the kick point).

• Weight. Too much weight decreases the club head speed, whereas too little increases the launch angle and spin rate.

• Stiffness. Too much stiffness lowers the ball’s speed and trajectory. Too much flexibility increases the ball’s trajectory.

• Flex point. The flex point is the region in which the club bends the most during the downswing, and the point at which it stores the most energy. In other words, the flex point puts the spring into the swing. Lowering the kick point increases the trajectory, while raising the kick point lowers the trajectory.

The DG Pro line is an example of how the company uses these manufacturing capabilities to tailor a set of irons. Based on customer feedback, True Temper developed this line of shafts to provide a little more lift to the long irons, which normally have low trajectories, and a little less to the short irons, which normally have high trajectories. The manufacturing process, which the company calls variable wall technology (VWT), allowed the designers to change the long irons by using more material near the grip and less near the head to increase the tip’s responsiveness, increasing the ball’s trajectory. For the short irons, they did the opposite, reducing the material near the grip and increasing it near the tip, stiffening the area near the head of the club. The result is a cushioned feel, a little more spin, and slightly lower ball flight.

This product line sums up the capability of variable-wall technology, helping the shaft and head designers develop products that help golfers get better distance, accuracy, and feedback.

Taking Stock. True Temper’s VWT shafts are made from 4140 steel with a yield strength of 60,200 PSI and an ultimate tensile strength of 95,000 PSI. True Temper starts with coil around 31⁄8 in. wide and runs it through a tube mill to make 1-in.-OD welded tube. It then uses a succession of drawing and annealing passes to bring it down to the necessary size. It also uses the combination of drawing and tempering to reduce the evidence of the weld seam as much as possible.

“We can’t have a spine in the shaft,” Cokeing said. A prominent weld seam would have a severe impact on performance. The club would be unstable, oscillating every time it was used, and unless every weld seam on every club in the set had the same orientation, the performance would vary wildly from one club to the next.

At this point—after 160 discrete manufacturing steps—the tube doesn’t look much like a golf club shaft. It’s just a blank with an OD of 0.650 in. and little strength. The next 30 or so steps turn this flimsy tube into something useful.

The next step is the drawing step that imparts the varying wall. The key to this process is the tooling.

“The mandrel is a tapered plug,” Cokeing said.

The mandrel imparts a single profile, again and again, as the material moves through the draw bench. The mandrel oscillates forward and backward in a motion coordinated with the forward motion of the tube stock. The result is a length of tube with a wall thickness that varies from one end to the other.

After a cut-to-length operation, the shaft goes through a few more steps. Many clubs have steps in the OD, which are made by inserting the shaft into a series of carbide dies. The shaft also goes through a heat-and-quench process that increases the material’s ultimate tensile strength to about 225,000 PSI. After straightening, finishing, polishing, and inspection, the shafts are packed and shipped. Most golfers would be surprised to learn that each golf club shaft is made from material that initially was 31⁄8 in. wide by about 4 in. long.

The efforts that go into controlling each step of the process—forming, welding, and the series of alternating drawing and annealing operations—culminate in cutting to length. Getting the cut length just right is among the trickiest steps in making 16 or 17 usable shafts. If it goes wrong, the outcome is 16 or 17 scrapped tubes. Cokeing doesn’t divulge how the cut length is controlled, but the weight tolerance says it all. The company’s products are categorized in three weight classes: ultralight (75 grams to 110 grams), midrange (110 to 120 g), and tour (120 to 135 g), and the weight tolerance is ±1.5 g. That’s not much weight. A penny weighs 2.5 g.

How does all this work pay off? The shaft stores quite a bit of energy, and when that energy is released, it makes a big difference between the club’s head speed and the ball launch speed. On the professional tour, the fastest club head speeds are between 125 and 130 MPH, and the fastest ball speeds are more than 45 percent faster, topping out around 190 MPH.

It pays off in another way. True Temper estimates that more than 70 percent of players on the Professional Golfers Association (PGA) Tour use clubs with shafts that have variable-wall technology.

Golf Then and Now

It’s rare that any modern activity, whether it’s a serious sport, a light-hearted game, or a relaxing leisurely pursuit, has modern roots. Nearly every game can be traced back hundreds of years, if not thousands, and golf is no different. Golf’s possible predecessors include many games that were played with sticks and clubs to strike wooden balls or stuffed leather balls, such as paganica (Rome), cambuca (England), chambot (France), chaugán (Persia), chuiwan (China), and kolven (Netherlands).

Regardless of its possible origins, the modern game developed in Scotland in the 15th century. The oldest course, at St. Andrews, initially consisted of 11 holes. A full game consisted of playing the 11 holes out and back for a total of 22 holes. Eventually some of the holes were determined to be too short and were combined, which led to the standard 18-hole course.

The course at St. Andrews also set the bar for hazards. While most courses have their fair share of obstacles, St. Andrews has several that vary from merely unique to mildly startling, including a stone wall, a road, and a 10-ft.-deep trap

(Hell Bunker). On most courses that have been designed and developed since then, the obstacles have become less challenging and less varied. Most golfers aren’t likely to deal with anything other than water hazards, sand traps, and rough areas to the left and right of the fairways.

The hazards aren’t the only things that have changed since the modern game developed 600 years ago. The clubs, once entirely made from wood, were updated when iron heads were developed in the middle of the 19th century. Steel shafts were introduced shortly thereafter, and another shaft material, graphite, emerged in the 1970s.

More so than the materials, the designs of the heads and shafts have multiplied terrifically. Most obvious are the many variations of heads, but the shaft design is just as varied, if not more so. True Temper alone has more than 4,000 golf club shaft designs.

Of course this doesn’t mean that the development work is finished. Far from it. Manufacturing is always progressing, so golfers can always look forward

to something new on the horizon. It might be a different alloy; an adjustment to the tempering process; or, because of variable-wall technology, a new shaft profile.

About the Author
FMA Communications Inc.

Eric Lundin

2135 Point Blvd

Elgin, IL 60123

815-227-8262

Eric Lundin worked on The Tube & Pipe Journal from 2000 to 2022.